My mother-in-law's heat has stopped working. The unit is an older model combo heat/ac outside unit, the type used on mobile homes. Can anyone tell me what to troublshoot to figure out what is the problem. I have checked the elements and they are clean and not rusted. They also have good resistance so I believe it is a relay or switch causeing the fault.

Well this is not a good diy project because of high voltage presence and you can be shocked very easily with these units.That being said you have 240 volt heating elements I am sure. If you have to ask this question I would not pursue this repair any further on your own electric heat can be tricky. I am still learning and have made plenty of mistakes along the way so don't think I am talking down to you, these electric furnaces are hazardous .

Has the heat worked this season or is this the first time you have used it this heating season? Could you give the make and model of both the outdoor condenser (heat pump?) and indoor air handler units? Did you check the circuit breaker at the air handler heat strips (I am assuming there are heat strips) and at the main circuit breaker box? Has any work been done on this unit within that past few months?

The unit is a combination AC/Heater(electric Heat Strips) for a mobile home. There is no inside air handler. It ran good at the beginning of the year and started to become less effecient to the point where the heat strips would not come on. I checked all fuse and circuit breakers, had no issues. I am pretty sure that the switch is bad(black device with about 6 or 8 connectectors coming out of it, with two wires going to the heat strips. I just want to verify if possible by conducting a continuety check. As far as being worried about my skills I am very cautious when working with electricity. Use to be in the construction and remodel business. Just trying to help my mother in law save some money.

Continuity can be tricky. IF, and I mean IF, it's possible to easily disconnect the wires going to the heat strips from the switch, then you can try for a continuity test. BE SURE all power if off at the circuit breaker. You need to electrically isolate the heat strips from the switch to make the test.

Another way would be to measure the voltage going to the heat strips. Again, be very careful and be sure the connections at the black switch are easy to get to with the multimeter probes. Assuming 240 volt heat strips, you should see 240 volts, AC across the two leads going to the strips. And you should see 120 volts, AC between each lead and the system ground/neutral.

So here we go, got a new sequencer and replaced the old one. The old one was no good it fell apart when I took it off the unit. Like the previous post states, I had a bad wire end or two replaced them. Now the element comes on, I can physically see it, however it seems like to me it is still not working right cause I only see a very small amount of the element turn red(roughly 15%). Is this normal or is the element failing? I checked voltage at the overheat protection switch on each element it read 110V and also the voltage at the bottom of the elements that too had 110V. I had 220V accross elements, meaning top ad bottom of element. BTW it is a two element 10 KW heater.

Since I have no idea how the element is designed, it's very hard to say if what you are observing is normal. Some elements are one long conductor so when there's a break, nothing will get warm. Others may be elements in parallel which could allow some to get hot while others don't.

Since this is an old furnace I would explore the possibilities of buying new elements. To check the existing ones you'll need to remove them anyway and bench test them.